Liquid dispenser for oscillating distilling column, and corresponding distilling column

ABSTRACT

This liquid distributor includes: 
     a primary distributor ( 13 ) including liquid-distribution openings and delimiting N 1  first compartments ( 22 ), each provided with liquid feed elements means ( 10, 11 ); and 
     a secondary distributor ( 14 ), arranged under the primary distributor ( 13 ) and including a dish with openworked perforated bottom which occupies substantially the entire cross-section of the distillation column ( 2 ), this dish being subdivided by partitions ( 25 ) into N 2  second compartments ( 24 ), with N 2&gt; N 1.

FIELD OF THE INVENTION

The present invention relates to a liquid distributor for oscillatingdistillation column. It applies in particular to the air distillationcolumns on board floating structures such as offshore oil platforms orbarges.

BACKGROUND OF THE INVENTION

Offshore oil platforms produce residual gases. For economic andenvironmental reasons, it is becoming more and more necessary to recoverthese gases. One method consists in converting them into heavierhydrocarbons, which are in liquid form and are therefore easier totransport, using the Fischer-Tropsch process which consumes largeamounts of oxygen.

It would therefore be beneficial to be able to install an airdistillation column on board a platform or a barge, but proper operationof equipment of this type is compromised by serious difficulties.Specifically, a first imperative is for the liquid to be distributeduniformly at the column head over the entire cross-section of thelatter, despite the oscillations of its axis due to the motion of thewaves.

SUMMARY OF THE INVENTION

The object of the invention is to provide a liquid distributor whoseoperation has very little sensitivity to oscillations of this type.

To that end, the invention relates to a liquid distributor foroscillating distillation column, characterized in that it comprises:

a primary distributor including liquid-distribution openings anddelimiting N1 first compartments, with N1 ≧2;

means for the balanced feeding of liquid to each of the firstcompartments; and

a secondary distributor, arranged under the primary distributor andcomprising a dish with openworked perforated bottom which occupiessubstantially the entire cross-section of the distillation column, thisdish being subdivided by partitions into N2 second compartments, with N2>N1;

the ratio of the area of each second compartment to the sum of thecross-sections of the openings of the primary distributor which feed itbeing substantially constant from one second compartment to another.

The distributor according to the invention may have one or more of thefollowing characteristics:

all the second compartments have substantially the same area and thesame perforation factor;

the number N1 is less than 5 and the number N2 is of the order ofseveral tens;

the primary distributor comprises a primary dish whose perforated bottomhas the same configuration as that of the secondary dish and issuperposed with the latter;

the said feed means comprise a phase separator and a feed conduitconnected upstream to the lower part of this separator and downstream totubes which are perforated plumb with each of the first compartments,the ratio of the area of a first compartment to the sum of thecross-sections of the corresponding perforations of the tubes beingconstant from one first compartment to another;

the tubes are tapped at points adjacent to the feed conduit and haveorifices adjacent to the central axis of the distributor;

the said feed means comprise a phase separator and perforated tubeswhich are connected to adjacent points of the lower part of theseparator.

The invention also relates to a distillation column comprising adistributor as defined above.

In one embodiment of such a distillation column, the said liquiddistributor is arranged at a first level of the column, in particular atthe column head, and the column includes, at at least one second level,a second liquid distributor as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described with reference tothe appended drawing, in which:

FIG. 1 schematically represents an oscillating distillation column whichis equipped with two liquid distributors according to the invention andis on board a floating structure;

FIG. 2 schematically represents, on a larger scale and in section on theline I—I in FIG. 3, the head distributor of the distillation column inFIG. 1;

FIG. 3 is a plan view of this distributor; and

FIG. 4 is a view taken in section on the line IV—IV in FIG. 2.

DETAILED DESCRIPTION

The distributor 1 represented in FIGS. 2 to 4 is intended to be mountedat the head of an air distillation column 2 which is schematized in FIG.1 as being the low-pressure column of a double air distillation column.

The column 2 is fixed on a floating structure 3, schematized in FIG. 1,as is the medium-pressure column of the double distillation column (notshown). FIG. 1 only shows the elements which help in understanding thepresent invention, although the double column obviously has all theelements which are conventional in the art.

More particularly, the column 2 is subdivided into an upper distillationsection 4 and a lower distillation section 5, both consisting ofcross-corrugated packing. As is well known, this type of packingincludes superposed cross-corrugated packing sections or packs 6, eachof which is in the form of a cylindrical slab occupying the entirecross-section of the, column.

Each pack 6 consists of a stack of corrugated strips with obliquecorrugations. Each strip has a vertical general plane, all the stripshave the same height, and the corrugations are alternatively inclined inone direction and in the other from one strip to the next. Thecorrugations of adjacent strips thus touch at a large number ofintersection points. Furthermore, the packs 6 are offset angularly by90° from one pack to the next relative to the general axis of thecolumn. Above the upper section 4, the column contains a distributor 1as described below, which is the head distributor 1A of the column. Asimilar second distributor, which constitutes an intermediatedistributor 1B, is arranged below the section 4 and above thedistillation section 5.

In service, “lean liquid” (almost pure nitrogen drawn from the head ofthe medium-pressure column) which arrives via a feed conduit 7 and isrelieved to the pressure of the column 2 in a pressure-reduction valve8, is introduced into a phase separator 9. The liquid collected in thelatter is introduced, via a feed manifold 10 connected to the lower partof the separator, into two parallel tubes 11 each of which has two lowerorifices 111. These two tubes are arranged in the upper dome 102 of thecolumn and form the liquid feed means of the distributor 1A. Thedistributor 1A distributes this liquid over the entire cross-section ofthe upper pack 6 of the distillation section 4, in a manner which willbe described below.

The oxygen-enriched liquid delivered by this section 4 falls, throughoutthe lower surface of this section, onto the intermediate distributor 1B.Furthermore, “rich liquid” with the same composition (oxygen-enrichedair collected from the base of the medium-pressure column), which isobtained from the medium-pressure column via a conduit 12, is added tothis liquid by means of an assembly formed by a pressure-reduction valve8, a phase separator 9, a manifold 10 and tubes 11, which is identicalto the one described above. The liquid is redistributed in full by thedistributor 1B over the entire cross-section of the column, to form thereflux of the lower distillation section 5.

The structure of the distributors 1A and 1B will now be described withreference to FIGS. 2 to 4.

The distributor 1A consists of two parts, namely a primary distributor13 and a secondary distributor 14 which is arranged underneath, andaforementioned feed means 9 to 11.

The primary distributor 13 has a dish which is open at the top, has ahorizontal bottom 15 and a cylindrical peripheral wall 16 which risesfrom this bottom. The bottom 15 has six slots 17 with a shape elongatedin the direction parallel to the tubes 11, which leave free, on theother hand, five strips parallel to the said direction. This ring andthese strips are perforated by a large number N of holes 18, which havea diameter sufficient to prevent any risk of obstruction by impuritiescontained in the liquid to be distributed. The number N is typically ofthe order of 1000 to 3000 for a column with a diameter of 4 m.

Each slot 17 is surrounded in full by a vertically rising wall 19 which,with the peripheral wall 16, delimits five straight funnels 20 plumbwith the aforementioned strips and a peripheral annular funnel 21 whichcommunicates with all the funnels 20.

Furthermore, the dish is subdivided into four compartments 22 of equalarea by two mutually perpendicular vertical partitions 23 whichintersect on the central axis X—X of the dish, which coincides with thecentral axis of the column 2. One of the partitions 23 passes throughthe middle plane of the central funnel 20.

The tubes 11 are adjacent to one another and are arranged plumb with thethird funnel 20, on either side of the partition 23 which divides it,with one orifice 111 each opening into each of the correspondingcompartments 22, in immediate proximity to the intersection of thepartitions 23. As a variant, there could be a plurality of orifices percompartment, and optionally more than two tubes 11, the essentialfeature being, on the one hand, that the sum of the cross-sections ofthe orifices which open into each compartment is the same, and on theother hand that all the orifices are close to one another so that theyremain at similar levels when the column is inclined.

The secondary distributor 14 is identical to the primary distributor 13apart from two differences.

On the one hand, the partitions 23 are absent. On the other hand, thefunnels 20 and 21 are subdivided into many more than four secondarycompartments 24 by a set of vertical partitions 25 which extend betweenthe walls 19 and between the latter and the peripheral wall 16. Thenumber of compartments 24, and the way in which they are arranged, willbe chosen so that they all have the same area and the same perforationfactor, as well as a maximum dimension at most equal to about 300 mm.

The primary 13 and secondary 14 distributors are directly superposed,that is to say each wall 16 or 19 of one of them lies in the verticalextension of the corresponding wall of the other. The upper edges of atleast some of the walls of the secondary distributor are fixed to thebottom 15 of the primary distributor, so as to form a monobloc assembly.

The distributor 1B is identical to the distributor 1A, apart from thefact that, in the primary distributor 13, the pairs of parallel walls 19which surround the adjacent funnels 20 are connected at their upper endby double-sloping roofs 26 and have a horizontal row of openings 27 justbelow these roofs, as indicated by dot/dash lines in FIG. 2.

In service, the liquid descending in the column 2 is in exchange contactas regards matter and heat with the oxygen gas obtained by heatingliquid oxygen, collected from the base of the column 2, through nitrogengas from the head of the medium-pressure column. This gas becomesprogressively enriched with nitrogen as it rises in the column 2.

The gas flows have not been represented in FIG. 1 for the sake ofclarity. However, it will be understood that the rising gas passeswithout difficulty through the distributors 1A and 1B via the slots 17and the openings 27, as schematized by arrows in FIG. 2.

When the structure 3 is at sea, the axis of the column 2 oscillatesabout its normally vertical position. The terms horizontal and“vertical” used above to describe the distributor 1 should be understoodas referring to this central position of the column, but when the latteris inclined, the bundle of tubes 11, the bottoms 15, the walls 16 and 19and the partitions 23 and 25 become inclined by the same angle.

By virtue of the partitioning of the secondary distributor into multiplecompartments 24 of smaller size, the difference in level between theholes 18 of each compartment 24 remains very small for all positions ofthe axis X—X, the maximum inclination of which is typically between 5and 10°. Consequently, the depth of liquid above them varies little fromone hole to the other. It will further be noted that, at any time, thestrongly fed holes are close to weakly fed holes of an adjacentcompartment, so that these two flow rates are readily compensated in thesame region of the upper pack 6 of the distillation section lyingimmediately below.

The influence of the inclination on the uniformity with which the liquidis distributed is further reduced, on the one hand, through the balancedfeeding of the compartments 24 by the four primary compartments 22, theareas of which are four times less than that of the column 2, and on theother hand by the fact that, since the inclination varies periodicallywith a relatively short period typically of the order of 20 s, theaverage level in each compartment 24 does not have time to varysignificantly.

Furthermore, the proximity of the tubes 11 and of the orifices 111ensures balanced feeding of the compartments 22 in spite of theinclination of the axis X—X. This result could also be obtained, as avariant, by means of four tubes which start from four adjacent points onthe bottom of the separator 9 and each have an orifice 111 which opensplumb with a respective compartment 22.

In total, distribution of the liquid with satisfactory uniformity isobtained over the entire cross-section of the column.

If desired, each compartment 22 may be equipped with means for remixingthe liquid, for example inclined partitions descending from the wall 16,as is known per se.

WO-A-90/10 497 describes, amongst others, packing which is similar tothe aforementioned cross-corrugated packing but is perforated in adifferent way. The term “cross-corrugated packing” used here alsocomprises such packing, as well as any similar packing.

What is claimed is:
 1. Liquid distributor for oscillating distillationcolumn, comprising: a primary distributor including liquid-distributionopenings and delimiting N1 first compartments, with N1≧2; means for thebalanced feeding of liquid to each of the first compartments; and asecondary distributor, arranged under the primary distributor andcomprising a dish with openworked perforated bottom which occupiessubstantially the entire cross-section of the distillation column, saiddish being subdivided by partitions into N2 second compartments, withN2>N1; the ratio of the area of each second compartment to the sum ofthe cross-sections of the openings of the primary distributor which feedit being substantially constant from one second compartment to another.2. Distributor according to claim 1, wherein the second compartmentshave substantially the same area and the same perforation factor. 3.Distributor according to claim 1, wherein the number N1 is less than 10and the number N2 is of the order of several tens.
 4. Distributoraccording to claim 1, wherein the primary distributor comprises aprimary dish whose perforated bottom has the same configuration as thatof the secondary dish and is superposed with the latter.
 5. Distributoraccording to claim 1, wherein said feed means comprise a phase separatorand a feed conduit connected upstream to the lower part of thisseparator and downstream to tubes which are perforated plumb with eachof the first compartments, the ratio of the area of a first compartmentto the sum of the cross-sections of the corresponding perforations ofthe tubes being constant from one first compartment to another. 6.Distributor according to claim 5, wherein the tubes are tapped at pointsadjacent to the feed conduit and have orifices adjacent to the centralaxis of the distributor.
 7. Distributor according to claim 1, whereinsaid feed means comprise a phase separator and perforated tubes whichare connected to adjacent points of the lower part of the separator. 8.Distillation column comprising a liquid distributor which comprises: aprimary distributor including liquid-distribution openings anddelimiting N1 first compartments, with N1≧2; means for the balancedfeeding of liquid to each of the first compartments; and a secondarydistributor, arranged under the primary distributor and comprising adish with openworked perforated bottom which occupies substantially theentire cross-section of the distillation column, said dish beingsubdivided by partitions into N2 second compartments, with N2>NM; theratio of the area of each second compartment to the sum of thecross-sections of the openings of the primary distributor which feed itbeing substantially constant from one second compartment to another. 9.Distillation column according to claim 8, wherein said liquiddistributor is arranged at a first level of the column, and the columnincludes, at least one second level, an additional liquid distributorwhich comprises: an additional primary distributor includingliquid-distribution openings and delimiting N1 additional firstcompartments, with N1≧2; means for the balanced feeding of liquid toeach of the additional first compartments; and an additional secondarydistributor, arranged under the additional primary distributor andcomprising an additional dish with openworked perforated bottom whichoccupies substantially the entire cross-section of the distillationcolumn, said additional dish being subdivided by partitions into N2additional second compartments, with N2>N1; the ratio of the area ofeach additional second compartment to the sum of the cross-sections ofthe openings of the additional primary distributor which feed it beingsubstantially constant from one additional second compartment toanother.
 10. Distillation column according to claim 9, wherein saidadditional primary distributor occupies substantially the entirecross-section of the column and is directly fed with a liquid output ofa distillation section located above said additional distributor. 11.Distillation column according to claim 8, wherein said column is onboard a floating structure.
 12. Distillation column according to claim11, wherein said floating structure is an offshore oil platform or abarge.